The effects of anoxia on isozyme patterns and ultrastructure of cultured human fibroblasts

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Abstract
Numerous studies with lower eukaryotes such as yeast and Neurospora have shown that mitochondrial morphology and enzyme levels change markedly in response to changes in oxygen tension. Several studies with mammalian cells in culture have indicated that these cells also respond to low oxygen with changes in the levels of certain enzymes. In this study gel electrophoretic analysis of enzymes and electron microscopic analysis of cell organelle morphology were used to study the effects of anaerobic conditions on cultured human embryo fibroblasts. Lactate dehydrogenase showed a marked shift from LDH‐1 toward LDH‐5 as has been previously described. Isocitrate dehydrogenase, NAD‐malate dehydrogenase, and NADP‐malate dehydrogenase all have been shown to exist as separate supernatant and mitochondrial isozymes. However, none of these enzymes showed extensive changes in isozyme patterns in response to anaerobiosis. Electron microscopic examination of cell cultures revealed striking changes in mitochondrial structure. Aerobically grown cells have well‐developed, elongated mitochondria with numerous well‐defined cristae and an electron‐dense matrix. In cells cultured anaerobically the mitochondria show degenerative changes. They are more rounded, have few and poorly defined cristae, and the matrix is more electronlucent. These studies indicate that, as in lower eukaryotes, the mitochondria of cultured human cells also respond morphologically and biochemically to changes in oxygen tension.